Neurophysiological correlates of bilingual advantage and its contribution to cognitive reserve

Project Information

BILINGUALPLAS

Grant agreement ID: 838536

DOI

10.3030/838536

Project closed

EC signature date 9 April 2019

Start date 1 January 2020

End date 22 April 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 172 932,48

EU contribution

€ 172 932,48

Coordinated by

BCBL BASQUE CENTER ON COGNITION BRAIN AND LANGUAGE
Spain

Periodic Reporting for period 1 - BILINGUALPLAS (Neurophysiological correlates of bilingual advantage and its contribution to cognitive reserve)

Reporting period: 2020-01-01 to 2021-12-31

Summary of the context and overall objectives of the project

In the last years, a hot topic in cognitive neuroscience is whether bilingualism contributes to improve executive functions (a set of cognitive processes such as ability to inhibit irrelevant information, switch attention between different stimuli, which are crucial to monitor goal directed actions) and increases cognitive reserve (CR, which involves optimised brain functioning). There are researchers stating evidence for bilingualism as a factor associated with enhanced executive functions and CR. However, a substantial number of studies failed to replicate enhanced executive functions in bilinguals compared to monolinguals. These results led to some authors to argue against the existence of a relationship between bilingualism, executive functioning and CR. Clarifying whether bilingualism contributes to improve executive functions and CR is highly important because a great amount of research has evidenced that high level of CR is related to greater resistance against brain damage. For instance, several studies found that Alzheimer’s disease symptoms could be delayed for five years in high compared to low CR persons, which would help to keep quality of life in older adults and maintain the sustainability of public health systems.

There are a set of variables such as task difficulty and modality (i.e. visual vs. auditory tasks) as well as the presence of other CR factors in older adults, which could mask the existence of a bilingual advantage in executive functions. Thus, the main objective of the present research is systematically manipulating task difficulty (low vs. high), task modality (auditory vs. visual) and CR of the recruited participants (that is, we recruited low CR monolinguals, low CR bilinguals, high CR monolinguals, and high CR bilinguals) to examine whether auditory tasks with high difficulty level are more sensitive to enhanced executive functions in older adults bilinguals compared to monolinguals. Another main hypothesis of this research is that differences between monolinguals and bilinguals will appear in samples with low CR but not in samples of participants with high CR since other CR factors such as high education level and occupational status will be able to preserve executive functions regardless the number of spoken languages. As differences in neural processing may be not always evident at the behavioural level, we focused on behavioural and neurophysiological measures by means of electroencephalography (EEG) / event-related brain potentials (ERP) and magnetic resonance imaging (MRI).

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

At the beginning of the project we carried out a comprehensive review about ERP studies investigating neural modulations during the performance of tasks used to investigate executive functions. After revising those studies, we have established specific differences between monolinguals and bilinguals that should be observed to claim the existence of a bilingual advantage in executive neural processing. This study, which was published in the prestigious journal Neuroscience & Biobehavioral Reviews, is a very relevant review article due to the lack of consensus to interpret ERP differences between monolinguals and bilinguals (especially in the absence of differences in the behavioural performance). Also, I carried out additional theoretical work by conducting a very exhaustive review on how EEG/ERP, transcranial magnetic stimulation and functional MRI studies using the Simon (which represents one of the most used paradigms to study executive functions) contributed to understand executive neural processing in the human brain.

A widely overlooked issue is the impossibility to conclude that bilingualism contributes to CR on the basis of the relationship between bilingualism and executive functions because executive functions and CR are not equivalent constructs. Moreover, the neural correlates of CR are still poorly understood. So, we analysed a set of previously collected data (specifically, about 90 older adults, which were divided into high and low CR groups) to investigate the interplay between executive functioning (by using behavioural and event-related brain potential correlates) and CR (by means of graph theoretical analysis of complex networks, which provide measures of brain connectivity that is thought to be the compensatory mechanism in high cognitive elderly). So far, we have obtained several ERP correlates distinguishing between high CR and low CR and, in general, ERP latencies are faster and ERP amplitudes are larger in high compared to low CR group.

There are other methodological problems contributing to the lack of consensus among the researchers studying relationships between bilingualism, executive functions and CR such as the biased interpretation of any difference as enhanced executive processing in bilinguals or the use of small samples. In this context, I have published an opinion paper explaining some procedures that would help to achieve a consensus among the researchers. In that study, I argue for publishing Registered Reports within this field of research to prevent biased results interpretations and improving the implementation of the scientific method. According to this view, we have pre-registered the main body of the research related to this project in the peer-reviewed journal Psychophysiology. We are now collecting data (we have argued that 160 participants divided in low CR monolinguals, low CR bilinguals, high CR monolinguals and high CR bilinguals will be needed) and we expect to submit the full manuscript within the next 18 months.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

A comprehension review about how ERP correlates of executive functions are modulated was a very relevant research because it helps to formulate well-grounded hypotheses in the upcoming studies. This study is not only useful to research in the field of bilingualism but it serves also to studies trying to investigate how any other lifestyle variable (e.g. playing music, practising physical exercise) contributes to improve neural processing. Importantly, the approach of investigating relationships between ERP and functional connectivity correlates to establish a link between enhanced executive functions and higher CR is very innovative and overtakes simplistic views considering that enhanced executive functions in the group X regarding the group Y involves enhanced CR in the group X compared to Y. Finally, the pre-registered neurophysiological study investigating how CR of the participants as well as task difficulty and modality modulate the existence between bilingualism and enhanced behavioural and executive neural processing will help to disentangle some sources of variability contributing to disparity of results in the current research.

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